This study will quantitate the effects of a decrease in deformability of the red cell on tissue metabolism as measured by biochemical parameters. Deformability will be measured by the rapidity with which the red cell passes through a specific polycarbonate membrane. Rats will be burned over 40% of their dorsal surface by immersion in boiling water for 30 seconds. This procedure will cause the red blood cells to become non-deformable within 30 minutes. Blood will be withdrawn from the burned rat and injected into the aorta of another, non-burned rat. Normal blood volume will be maintained by removing as much blood as is infused. Experiments will be carried out during hypoxia and hypotension to mimic stressful clinical situations. The brain will then be removed and mitochondria will be isolated. Changes in mitochondrial function secondary to possible flow changes due to rigid red cells will be evaluated. The purpose will be to determine what effect, if any, rigid red cells have upon brain blood flow as evaluated by changes in mitochondrial energy metabolism.